Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists studying two big craters on earth find two causes

28.10.2002


Two of the three largest impact craters on Earth have nearly the same size and structure, researchers say, but one was caused by a comet while the other was caused by an asteroid. These surprising results could have implications for where scientists might look for evidence of primitive life on Mars.



Susan Kieffer of the University of Illinois at Urbana-Champaign, Kevin Pope of Geo Eco Arc Research and Doreen Ames of Natural Resources Canada analyzed the structure and stratigraphy of the 65 million-year-old Chicxulub crater in Mexico and the 1.8 billion-year-old Sudbury crater in Canada.

Chicxulub is well preserved, but buried, and can be studied only by geophysical means, remote sensing and at a few distant sites on land where some ejecta is preserved. In contrast, Sudbury has experienced up to 4-6 kilometers of erosion, and is well exposed and highly studied by mining exploration companies because of its rich mineral resources.


By working back and forth with data from the two craters, the researchers were able to re-create the structures and then estimate the amount of melt in each structure. The amount of melt is critical for determining if long-lived hot-water circulation systems that might host life forms could have been formed after the impacts.

In their field studies, the researchers found that both craters were about 200 kilometers in diameter. In addition, they identified five ring-shaped structures with similar character and dimensions. A sixth ring -- the peak ring in the central basin -- was present at Chicxulub, but had been eroded away at Sudbury.

"While the size and structure of the two craters were similar, they differed greatly in the amount of impact melt that was produced," said Kieffer, who presented the team’s findings at the annual meeting of the Geological Society of America, held Oct. 27-30 in Denver.

"Through field studies, we determined that Chicxulub has about 18,000 cubic kilometers of impact melt, approximately four times the volume of water in Lake Michigan," Pope said. Sudbury has about 31,000 cubic kilometers of impact melt, approximately six times the volume of lakes Huron and Ontario combined, and nearly 70 percent more than the melt at Chicxulub. These differences in volume have significant implications about the amount of heat available to drive hot-water circulation systems.

The researchers then used an analytical cratering model to examine possible causes for the huge difference in melt. According to the simulation results, the difference in melt volume could be readily explained if Chicxulub -- the impact crater that doomed the dinosaurs -- was formed by an asteroid and Sudbury was formed by a comet.

"Our calculation of 18,000 cubic kilometers of impact melt at Chicxulub agreed well with model estimates for an asteroid striking at a 45 degree angle," said Kieffer, the Walgreen Professor of Geology at Illinois. "None of the comet impact examples came close to agreeing."

"In contrast, the Sudbury impact melt volume of 31,000 cubic kilometers fell between model estimates for a comet striking at an angle of 30-45 degrees", Kieffer said. "Similarly, none of the asteroid impact examples came close to agreeing with the Sudbury melt volume."

Another clue to the cratersÕ origins lies in the impact melts themselves. The majority of the excess melt at Sudbury is in the form of a melt-rich breccia Ð called suevite Ð inside the crater. This material tends to form in impacts where the crustal target rock contains a lot of water. Sudbury has much more suevite in the preserved crater than Chicxulub.

"The mystery was that there probably wasn’t a lot of water in the original rocks at Sudbury to account for the excess suevite," Kieffer said. "But in a comet impact of this size, somewhere around 1,400-2,000 cubic kilometers of water from the comet gets mixed into the impact melt, and that could play a major role in disrupting the melt and creating the excess suevite."

There is other independent evidence for an asteroid impact at Chicxulub, the team said, including the purported find of an asteroid fragment in an oceanic drill core, the amount of iridium spread around the world at the time of impact, and a telltale chromium 53 isotopic signature.

By studying the origin and structure of large impact craters on Earth, scientists might narrow the search for life on Mars. At Sudbury, for example, "there is evidence of a huge hydrothermal system that was driven by the heat of the impact melt," Ames said. "As a result, there was widespread hot spring activity on the crater floor possibly capable of supporting life."

The researchers are interested in "extrapolating these conclusions about comet and asteroid impacts to Martian conditions and asking where we might go to look for similar hydrothermal systems that could have hosted primitive life forms on Mars," Kieffer said. "Our next step is to model these hot-water circulation systems that were set up by the impact melts with fluid flow controlled by structures (fractures) inside the crater, and then extrapolate the results to Martian conditions."

The National Aeronautics and Space Administration and the Natural History Museum of Los Angeles County funded this work

James E. Kloeppel | EurekAlert!
Further information:
http://www.uiuc.edu/

More articles from Earth Sciences:

nachricht Geomagnetic jerks finally reproduced and explained
23.04.2019 | CNRS

nachricht "Flight recorder" of rocks within the Earth’s crust
16.04.2019 | Universität Bern

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Quantum gas turns supersolid

Researchers led by Francesca Ferlaino from the University of Innsbruck and the Austrian Academy of Sciences report in Physical Review X on the observation of supersolid behavior in dipolar quantum gases of erbium and dysprosium. In the dysprosium gas these properties are unprecedentedly long-lived. This sets the stage for future investigations into the nature of this exotic phase of matter.

Supersolidity is a paradoxical state where the matter is both crystallized and superfluid. Predicted 50 years ago, such a counter-intuitive phase, featuring...

Im Focus: Explosion on Jupiter-sized star 10 times more powerful than ever seen on our sun

A stellar flare 10 times more powerful than anything seen on our sun has burst from an ultracool star almost the same size as Jupiter

  • Coolest and smallest star to produce a superflare found
  • Star is a tenth of the radius of our Sun
  • Researchers led by University of Warwick could only see...

Im Focus: Quantum simulation more stable than expected

A localization phenomenon boosts the accuracy of solving quantum many-body problems with quantum computers which are otherwise challenging for conventional computers. This brings such digital quantum simulation within reach on quantum devices available today.

Quantum computers promise to solve certain computational problems exponentially faster than any classical machine. “A particularly promising application is the...

Im Focus: Largest, fastest array of microscopic 'traffic cops' for optical communications

The technology could revolutionize how information travels through data centers and artificial intelligence networks

Engineers at the University of California, Berkeley have built a new photonic switch that can control the direction of light passing through optical fibers...

Im Focus: A long-distance relationship in femtoseconds

Physicists observe how electron-hole pairs drift apart at ultrafast speed, but still remain strongly bound.

Modern electronics relies on ultrafast charge motion on ever shorter length scales. Physicists from Regensburg and Gothenburg have now succeeded in resolving a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

First dust conference in the Central Asian part of the earth’s dust belt

15.04.2019 | Event News

Fraunhofer FHR at the IEEE Radar Conference 2019 in Boston, USA

09.04.2019 | Event News

 
Latest News

Marine Skin dives deeper for better monitoring

23.04.2019 | Information Technology

Geomagnetic jerks finally reproduced and explained

23.04.2019 | Earth Sciences

Overlooked molecular machine in cell nucleus may hold key to treating aggressive leukemia

23.04.2019 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>